The first two minutes after starting a cold engine are decisive for emission of pollutants in the exhaust gases of an internal combustion engine. It is in this period that about 70-80% of the total emissions of HC and CO are discharged. Because the catalytic converter has not yet reached its operating temperature within this time period, the engine discharges virtually raw emissions.
Various means are known for shortening this period, for example, by using a burner system to heat the catalytic converter as disclosed in DE-A-22 19 371, in an attempt to achieve operational readiness more quickly after a cold start.
Irrespective of the construction and mode of operation of the burner system, conventionally, the raw exhaust gases of the internal combustion engine are mixed with hot gases from the burner system before the exhaust gas mixture enters the catalytic converter. As the catalytic converter ages, it is known that impairment in its operation starts at the front or inlet of the catalytic converter for engine exhaust gases. When such aging occurs, the catalyst in the catalytic converter is heated at the inlet by the hot gases from the known burner system, but this has little effect on the conversion rate of pollutant reduction as the operation of the catalytic converter at its inlet end is the first to be impaired and the remaining part of the catalytic converter is not yet sufficiently heated to reach an efficient operating temperature. As a result, the discharged exhaust gases comprise virtually raw emissions.